The invention relates to a seat belt retractor having a function of retracting a seat belt by a motor.
In a seat belt to be used in a vehicle or automobile, a tension is applied by a seat belt retractor. In other words, in case the seat belt is used, one end of a seat belt wound by a spring in the seat belt retractor is drawn out by a passenger and engaged with another side of the seat belt fixed to a seat through a buckle. Thereafter, when the passenger releases the hands from the seat belt, the loosened seat belt is wound up by an action of the spring in the seat belt retractor, and a tension determined by the spring is provided to the seat belt to thereby hold the passenger to the seat.
However, in such a spring-type retracting mechanism, since a force is applied only in a seat belt tightening direction, in case the passenger tries to loosen the seat belt, the passenger has to pull out the seat belt against the force. Also, since an elasticity of the spring is used in retracting the seat belt, the operation is unstable, which may result in a poor seat-belt retraction.
To solve the above problems, there has been proposed a seat belt retractor, wherein a seat belt is wound by a motor. More specifically, an engagement of a buckle and a tongue plate fixed to the seat belt is electrically detected, and in case a disengagement thereof is detected, the seat belt is wound by a motor. In other words, while the buckle and the tongue are engaged with each other, it is assumed that the passenger wears the seat belt, so that retraction of the seat belt is not carried out by the motor and is carried out by a spring with a weak force. In some cases, the seat belt may be retracted only by a motor with a weak retracting force without using the spring.
However, when the seat belt is in an operating condition, in addition to the normal operation, there may be a situation wherein the seat belt has to be retracted with a larger torque than normal. For example, in case a collision is detected beforehand, it is required that the looseness of the belt is quickly wound up and the passenger is held to a seat with a stronger force than normal. Also, in case a child seat is fixed to a seat by the seat belt, it is necessary to firmly fix the child seat with a stronger force than that required for holding the passenger to thereby require a large torque. In the present specification, this type of retracting condition is called as a xe2x80x9cforced retractionxe2x80x9d and is distinguished from a xe2x80x9cnormal retractionxe2x80x9d.
In case the forced retraction and the normal retraction are carried out by one motor, a torque control and a speed control of the motor have to be performed. An example thereof is shown in FIG. 4. Though not shown, a motor M is connected to a seat belt retractor, and the seat belt is wound or unwound through rotation of the motor M.
Control pulses P1-P4 are outputted from a central processing unit (hereinafter referred to as xe2x80x9cCPUxe2x80x9d) and are provided to gates of switching transistors Q1-Q4 which are switching elements as P1xe2x80x2-P4xe2x80x2 through a gate circuit GATE. On the other hand, a voltage from a direct current (hereinafter referred to as xe2x80x9cDCxe2x80x9d) power source is connected to collectors of the switching transistors Q1, Q2; a motor terminal A is connected to an emitter of the transistor Q1 and a collector of the transistor Q4; and a motor terminal B is connected to an emitter of the transistor Q2 and a collector of the transistor Q3. Further, emitters of the switching transistors Q3, Q4 are grounded.
When the buckle of the seat belt is engaged with the tongue plate, and external information, such as a rotating direction and rotating speed of the motor M, is inputted, the CPU outputs control pulses P1-P4 corresponding thereto. A rotating direction of the motor M is determined by the on/off operation of the control pulses P1-P4, and a rotating speed of the motor M can be changed by varying duty ratio of the control pulses.
Incidentally, in FIG. 4, a thermistor TH is provided to monitor a temperature of the motor M, and when the temperature of the motor M is raised due to an overload thereof, the information thereof is inputted into the CPU to stop driving of the motor M. A flywheel diode connected parallel to the motor M is omitted in the drawing.
As described hereinabove, according to the circuit shown in FIG. 4, since the seat belt can be driven at a necessary speed and in a necessary direction, the forced retraction and normal retraction can be made by one motor. However, in that case, the normal retraction is carried out with a small duty ratio, which results in a poor control ability. In reality, in case the normal retraction is carried out, the duty ratio thereof should be set with a certain larger number, and switching transistors having smaller capacities for that duty ratio may be used. However, when the forced retraction is also carried out by the switching circuit, switching transistors having larger capacities are required, which results in a high cost of the circuit.
Also, in case rotation of the motor is controlled by the duty ratio, i.e. a pulse width, a high-cost switching circuit, i.e. speed control circuit, is required, and at the same time, noises are generated from the switching circuit and the control circuit. To prevent the noises from entering a power source circuit, a filter circuit with a large capacity is required, which results in a high cost of the entire device.
In view of the above problems, the present invention has been made, and an object of the invention is to provide a seat belt retractor, wherein a forced retraction and normal retraction can be carried out with an economical structure without requiring a filter with a large capacity.
Another object of the invention is to provide a seat belt retractor as stated above, wherein the normal retraction can be carried out easily through a logic circuit, the forced retraction can be carried out by a simple circuit and operation can be firmly done.
Further objects and advantages of the invention will be apparent from the following description of the invention.
In order to attain the above objects, according to a first aspect of the invention, a seat belt retractor having a function for retracting a seat belt by motors includes a first motor for retracting the seat belt with a force not providing a pressing feeling to a passenger, and a second motor for retracting the seat belt with a force strongly holding the passenger to a seat, and these two motors are controlled by a control circuit.
In the first aspect, a normal retracting motor, i.e. the first motor, and a forced retracting motor, i.e. the second motor, are separated to simplify the control circuit. In other words, since a speed control and a torque control are not required to be carried out in the control circuit, the control circuit is simplified, and at the same time, noises generated according to switching can be removed. Thus, a filter for preventing the noises from entering a power source is not required, or even if required, its size is small. Through control of the single control circuit, the respective motors can move without inconsistency.
According to a second aspect of the invention to attain the above objects, in the first aspect, the first motor is controlled through a logic circuit formed of a microcomputer or a semiconductor circuit, and the second motor is directly driven through a switching circuit controlled by an external signal not through the logic circuit formed of the microcomputer or the semiconductor circuit.
In the motor for carrying out the normal retraction, in addition to a situation such that a retraction is carried out under disengagement of a buckle and a tongue plate, for example, when it is detected that the passenger gets off, i.e. no passenger is in the automobile, a logic for carrying out re-retracting may be added. It is preferable to easily change the logic. Thus, the control of the first motor is carried out through the logic circuit formed of the microcomputer or semiconductor circuit.
On the other hand, it is preferable that the motor for carrying out the forced retraction is directly driven by a simpler circuit since it is required to operate at an emergency time such that a collision is expected. Thus, in the second aspect, the forced retraction is directly made through the switching circuit controlled by the external signal.
According to a third aspect of the invention to attain the above objects, in the first or second aspect, there is provided an interlock so that a power is not supplied to the first and second motors simultaneously.
In considering an unusual combination in a logic circuit, according to a combination in a logic circuit, it is undeniable that the first motor and second motor are simultaneously rotated in the opposite directions. When such a situation takes place, a retracting force in the forced retraction may be weakened. Also, in case an inspection work is carried out, there may be formed a forced retraction condition, and the forced retracting motor is driven. Thus, in the present aspect, there is provided an interlock for not supplying powers to the first motor and the second motor simultaneously to prevent such a situation.
According to a fourth aspect of the invention to attain the above objects, in the third aspect, the interlock is carried out by a circuit for not providing power to the second motor by an output from the microcomputer or semiconductor circuit for controlling the first motor.
In the fourth aspect, the interlock for not providing the power to the second motor is carried out by the output from the microcomputer or semiconductor circuit for controlling the first motor. Thus, the interlock for not providing the power of the second motor can be formed by a combination of complicated conditions.